Optical fiber cables have many designs for including multiple fibers within a single cable. Once such design is to include one or more “loose” tubes within a larger cable jacket, each of the tubes having one or more optical fibers loosely arranged therein. One such arrangement for these optical cables, shown in prior art FIG. 1, is for four tubes, each having twelve fibers therein, to be arranged within an outer jacket. Other elements are typically included within the outer jacket include strength members and binders.
The strength members are used to provide pulling tension support during installation of the cable, and binders are used to keep the multiple loose tubes in a central and tightly arranged configuration to protect against installation stresses caused by the bending and pulling of the cable. Typical binders are 2-3 mm in thickness, and may include a water swellable material (for added protection against moisture) and applied to the loose tubes, prior to jacketing under approximately 500-1000 grams of tension.
Another aspect of construction of cables of this sort is the selection of the polymers used to form the tubes and jacket. The selection of polymers for use in the tubes and jacket is a combination of cost, ease of use, crush resistance, environmental protection, installation flexibility, production quality (extrusion line speed), fire safety concerns etc. . . . .
One such factor that affects these issues is the Modulus (Young's Constant) of the polymer chosen. Polymers with a higher modulus, such as those in the range resulting in a tensile strength of 4,000-10,000 PSI, are suitable in such cables particularly for use in crush resistance and anti-compression.
However, when using these high modulus plastics, the associated expansion and contraction during thermal cycling (caused by exposure to hot and cold temperatures) imparts stress on the underlying fibers. Although binders, such as those shown in FIG. 1, may be used to secure the tubes to a central strength member to alleviate such an effect, such an arrangement has not proven affective and overcoming the problem.